In due sequence we must consider the vices opposed to commutative justice. We must consider (1) those sins that are committed in relation to involuntary commutations; (2) those that are committed with regard to voluntary commutations. Sins are committed in relation to involuntary commutations by doing an injury to one's neighbor against his will: and this can be done in two ways, namely by deed or by word. By deed when one's neighbor is injured either in his own person, or in a person connected with him, or in his possessions.
We must therefore consider these points in due order, and in the first place we shall consider murder whereby a man inflicts the greatest injury on his neighbor. Under this head there are eight points of inquiry:
(1) Whether it is a sin to kill dumb animals or even plants?(2) Whether it is lawful to kill a sinner?
(3) Whether this is lawful to a private individual, or to a public person only?
(4) Whether this is lawful to a cleric?
(5) Whether it is lawful to kill oneself?
(6) Whether it is lawful to kill a just man?
(7) Whether it is lawful to kill a man in self-defense?
(8) Whether accidental homicide is a mortal sin?